This invention relates to entrained flow coal gasifiers and in particular to a method and apparatus for obtaining a higher heating value gas therefrom.
Gasification of coal is primarily the incomplete combustion of the coal. The maximum heating value is theoretically obtainable by maintaining a minimum air or oxygen to coal ratio. The ability to achieve this, however, is restrained due to the relatively high temperature level required to maintain the endothermic coal gasifying reactions.
The entrained flow gasification process involves the suspension of coal or char particles in a hot gas stream formed by combustion of fuel. These particles then flow concurrently with the product gas stream. Since the particles are suspended in the stream, problems with oiliness and stickiness of the particles during the gasification do not cause problems of stickiness in the flow of the coal.
In such a process, when the gas temperature drops to the range of 1700.degree. to 2000.degree. F. the rate of gasification of the carbon particles diminishes to such a point that there is no practical value continuing the gasification process. Some of the high temperature level of heat which was available from the initial combustion of the fuel has been used to drive off volatiles and, therefore, is not available for effectuating the gasification of the char particles. While there is still substantial heat content in the gas stream, it is not available for the coal gasification operation and can only be used to generate steam for some other useful purpose.
It is an object of the invention to more effectively utilize the heat available so as to increase the heating value of the gas produced.